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A Novel Millimeter-Wave Dual-Fed Phased Array for Beam Steering

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A Novel Millimeter-Wave Dual-Fed Phased Array for Beam Steering A Novel Millimeter-Wave Dual-Fed Phased Array for Beam Steering Zur Erlangung des akademischen Grades eines DOKTOR-INGENIEURS von der Fakultat¨ fur¨ Elektrotechnik und Informationstechnik, am Karlsruher Institut fur¨ Technologie (KIT) genehmigte DISSERTATION von M.Sc. Ali Eray Topak geb. in Denizli, Turkei¨ Tag der mundlichen¨ Prufung:¨ 14. November 2013 Hauptreferent: Prof. Dr.-Ing. Thomas Zwick Korreferent: Prof. Dr.-Ing. Christian Waldschmidt Abstract A phased array antenna, used for shaping and steering the main antenna beam electronically to chosen directions within the predefined field of view, has been the key antenna system for satellite communications and military radars for decades. However, despite its high functional performance, it is still a very costly and complex solution for emerging wireless consumer applications such as high speed wireless communication and driving assistance systems due to the number of phase shifters and their complex control circuitry. Even more challenges are encountered with an increase in the number of channels if an antenna with high directivity is desired, such as routing RF and IF circuits, isolation of neighboring RF channels or calibra- tion of a whole system. In order to eliminate the challenges stated above, a novel beam steering approach is presented in this dissertation based on the superposition of two squinted antenna beams. The two an- tenna beams are realized by exciting the opposite feeds of a dual-fed array antenna. A change in the phase difference and amplitude ratio between the input signals, using only one phase shifter and two variable gain amplifiers or only two I-Q vector modulators, steers the main beam in different directions. Due to its similar architecture, it exhibits all the advantages that a traveling wave antenna possesses as well, such as beam steering with the change of the operating frequency. Additionally, the sum and difference patterns can be obtained using this concept, allowing for an amplitude-comparison monopulse operation with a broad peak or a deep null at the broad- side. Using this approach, beam nulls can also be steered towards interference directions, while keeping the shape and direction of the main beam unchanged. Another advantage is its high robustness against phase and amplitude errors due to analog hardware components in the RF path, which cannot be avoided in conventional phased arrays. A channel mismatch and crosstalk between neighbor RF channels or a temperature and time dependent array cali- bration can be minimized via this technique thanks to its unique topology, as well. In this work, an analytic antenna model has been derived and implemented in MATLAB us- ing closed form expressions to analyze and optimize each relevant antenna parameter. Using this model, the development time becomes significantly shorter and the required computer memory is almost negligible. In order to prove the validity of the proposed novel beam steering approach, two different millimeter-wave (mm-wave) dual-feed antenna setups have been designed and implemented. In the first setup, commercial passive WR-10 components are used to perform the phase and i - ii - amplitude changes manually. To demonstrate the full capability of electronic scanning, a second setup is built by employing an I-Q vector modulator instead of the waveguide phase shifter and the attenuator, which is controllable via input current signals. A mm-wave bare- die transceiver MMIC which houses an integrated I-Q vector modulator in its transmitter path has been characterized. For the transition of mm-wave signals from waveguide to planar RF board, a low-loss and broadband waveguide to microstrip line transition has been designed and realized. The measurement results of both setups show a beam scanning range of 16◦ using the phase shifter and an attenuator, well in accord with the simulation results. A monopulse antenna system has been realized for the sum and difference patterns using each test setup. Also, beam steering capability of the both setups has been demonstrated by changing the operating frequency. Even though the test setups have been realized for 77 GHz, this technique is ap- plicable at any frequency range. Zusammenfassung Phasengesteuerte Gruppenantennen (Phased Array Antennen), verwendet fur¨ die elektron- ische Formung und Ausrichtung der Antennen-Abstrahlcharakteristik bzw. des Antennen- hauptstrahls innerhalb des vorgegebenen Sichtfeldes, sind seit Jahrzehnten eine Schlussel-¨ technologie in der Satelliten-Kommunikation und bei militarischen¨ Radaranlagen. Doch trotz ihrer hohen funktionalen Leistungsfahigkeit,¨ sind sie immer noch eine sehr kostspielige und komplexe Losung¨ fur¨ neu entstehende drahtlose Anwendungen im Bereich der schnellen Datenubertragung¨ oder der Fahrerassistenz-Systeme, bedingt durch die benotigte¨ große Zahl von Phasenschiebern und deren komplexe Ansteuerung bei diesem Konzept. Noch mehr Her- ausforderungen ergeben sich mit der Erhohung¨ der Anzahl der Kanale,¨ wenn eine Antenne mit starken Richtwirkung erwunscht¨ wird, zum Beispiel bei der Verdrahtung von integrierte HF und ZF-Bausteinen, bei der Isolation benachbarter HF-Kanale¨ oder bei der Kalibration der gesamten Systemanordnung. Zur Bewaltigung¨ der oben aufgefuhrten¨ Herausforderungen wird in der vorliegenden Disser- tation ein neues Verfahren fur¨ die Formung und Ausrichtung der Antennenkeulen vorgestellt, basierend auf der Superposition zweier gegen die Antennennormale gedrehte Antennen- strahlen. Die beiden Antennenkeulen werden durch die gleichzeitige Anregung der Ein- speisepunkte einer zweiseitig einspeisbaren linearen Gruppenantenne (Dual Fed Antenne) erzeugt. Eine Anderung¨ der Phasendifferenz und des Amplitudenverhaltnisses¨ zwischen den beiden Anregungssignal mit Hilfe eines Phasenschiebers und eines Verstarkers¨ mit vari- abel einstellbarer Verstarkung,¨ oder stattdessen nur eines IQ-Vektor-Modulators, steuert den Hauptstrahl in verschieden Richtungen. Aufgrund der Ahnlichkeit¨ des Aufbaus mit dem einer Wanderwellenantenne (Traveling Wave Antennas), besitzt er alle Vorteile solcher Wander- wellenantennen, wie zum Beispiel die Steuerung der Hauptkeule mit der Betriebsfrequenz. Zusatzlich¨ lasst¨ sich das Summen- und Differenz-Antennendiagramm durch die Verwendung dieses Konzepts bestimmen, die einen amplitudenvergleichenden Monopulsbetrieb mit einem breiten Hauptstrahl oder einer Ausloschung¨ in Hauptrichtung der Antenne ermoglichen.¨ Mit diesem Verfahren konnen¨ auch Nullstellen im Antennendiagramm in Richtungen von Storern¨ gelegt werden, wahrend¨ die Form und Richtung der Hauptkeule erhalten bleibt. Ein weitere Vorteil ist die Robustheit des Verfahrens gegenuber¨ von Phasen- und Amplitudenfehlern die von der analogen Hardware im HF-Pfad kommen, welche bei konventionellen phasenges- teuerten Gruppenantennen nicht vermieden werden konnen.¨ Durch das beschriebene Ver- fahren konnen¨ eine Kanal-Fehlanpassung und ein Ubersprechen¨ zwischen benachbarten HF- Kanalen¨ verringert werden oder auch eine temperaturabhangige¨ und zeitabhangige¨ Kalibra- tion vermieden werden. In der vorgelegten Arbeit wurde ein analytisches Antennenmodell iii - iv - mit geschlossenen Ausrucken¨ entwickelt und in MATLAB implementiert, mit dem jeder rel- evante Parameter der Antenne analysiert und optimiert werden kann. Mit diesem Modell lasst¨ sich die Entwicklungszeit wesentlich reduzieren und der benotigte¨ Computer-Speicher ist nahezu vernachlassigbar.¨ Um die Gultigkeit¨ des neuen Steuerverfahrens des Antennendiagramms unter Beweis zu stellen, wurden zwei verschiedene Dual-Fed Antennen fur¨ Millimeter-Wellen entworfen und implementiert. Im ersten Aufbau werden kommerzielle passive WR-10 Hohlleiter- Komponenten benutzt, um die Phasen- und Amplitudenverschiebungen manuell vorzunehmen. Um die volle Leistungsfahigkeit¨ der elektronischen Abtastung zu demonstrieren, wird ein zweiter Aufbau realisiert, bei dem anstelle des Hohlleiter-Phasenschiebers- und Dampfungs-¨ gliedes ein IQ-Vektor-Modulator benutzt wird, der durch Eingangsstromsignale kontrollier- bar ist. Ein nicht gehauster integrierter Millimeterwellen Transceiver Chip (Transceiver MMIC), der einen IQ-Vektor-Modulator in seinem Sendepfad beherbergt, wurde charak- terisiert. Fur¨ die Transmission des Millimeterwellen-Signals vom Hohlleiter zur planaren Hochfrequenz-Platine wurde ein verlustarmer und breitbandiger Ubergang¨ vom Hohlleiter auf eine Mikrostreifenleitung entworfen und realisiert. Die Messergebnisse fur¨ beide Aufbauten zeigen einen Steuerungsbereich des Hauptstrahls uber¨ 16◦, wenn der Phasenschieber und das Dampfungsglied¨ benutzt werden, in guter Ubere-¨ instimmung mit den Resultaten aus der Simulation. Ein Monopuls-Antennensystem zur Erzeugung des Summen- und Differenz-Antennendiagramms wurde mit beiden Test- Anordnungen realisiert. Ebenso wurde die Strahlsteuerung durch Anderung¨ der Betriebsfre- quenz mit beiden Aufbauten bewiesen. Auch wenn die Test-Systeme fur¨ 77 GHz aufgebaut wurden, so ist diese Technik doch fur¨ jeden beliebigen Frequenzbereich anwendbar. Acknowledgments I would like to sincerely thank Prof. Dr.-Ing. Thomas Zwick, the director of Institut fur¨ Hochfrequenztechnik und Elektronik (IHE) at the Karlsruhe Institute of Technology, for his invaluable guidance and support during my work. Next, I would like to give my sincere thanks to Prof. Dr.-Ing. Christian Waldschmidt, the co-examiner and the director of Institute of Microwave Techniques at the University of Ulm for his careful review of my Ph.D. thesis. Particularly,
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